1. Field of the Invention
The present invention relates to a spark plug for an internal combustion engine.
2. Description of the Related Art
Conventionally, in a spark plug used for an internal combustion engine, especially for a reciprocating engine, a required voltage for generating a spark in a gap between a center electrode and a ground electrode opposed to the center electrode (hereinafter referred to as "required voltage") has become extremely high because of the recent trend for a lower fuel consumption. Therefore, insulation break is sometimes caused in ignition systems. It has been desired to discover technique for generating a spark having a low required voltage.
Inventions for providing the above technique are disclosed in Japanese Patent Publication No. 52-15739 and Japanese Patent Laid-open publication No. 51-66946.
In the spark plug disclosed in Japanese Patent Publication No. 52-15739, a first spark gap between a first ground electrode opposing an end face of a center electrode and the center electrode and a second spark gap between a second ground electrode disposed at approximately a right angle with the first ground electrode around the center electrode and outer peripheral surface of the center electrode are formed. However, the spark plug of the above invention has a problem that, when used for an internal combustion engine, the spark gap is increased by large consumption by the center electrode, and so the required voltage rises.
On the other hand, the spark plug, disclosed in Japanese Patent Laid-open Publication No. 51-66946, in which a spark gap is formed between a center electrode and a ground electrode opposing the center electrode, is provided with a groove extending to the end of the center electrode in an axial direction of the center electrode on the side surface of the center electrode forming the spark gap. However, this spark plug also has a problem that, when used for an internal combustion engine, the spark gap is increased by large consumption by the center electrode, and so the required voltage rises.